The use of hydraulic wrenches is widespread in the industry since the end of the last century as a result of their versatility and easy handling for performing large turning efforts. Furthermore, using hydraulic wrenches is the only viable option for small spaces or in tall assemblies with a high torque moment. In the beginning these operations were performed with torque wrenches, however the limitation is obvious since they depend on human strength and the ability to construct only levers with finite length for obvious reasons.
To overcome this drawback, mechanical torque multipliers were developed which as a result of using different types and sizes of gears successfully increases the torque in a considerable manner. The use of pneumatic cylinders is also common for increasing the force, but, for the use of large sections of screws, hydraulics is still the most comfortable, economical, transportable and capable way for exerting large tightening efforts in small spaces or difficult to access spaces.
Therefore, the development of these devices has been evolving in line with the use of screws according to the applicable regulations and the advances in the field of hydraulics. Their use is common in large installations which due to transport reasons need to be disassembled or due to access problems require the use of screws and nuts. They can thus be found in facilities where the use of such device is needed such as the oil industry, nuclear industry, heavy machine industry, mining industry, naval industry, wind energy industry, etc.
However, the use of the mentioned devices has the risk of breaks in its mechanisms or of wear of the threaded elements being handled, screws or nuts, due to the involvement of large actuating forces, especially when loosening is performed, where a large amount of energy which the components of the tools used in these operations must endure, is released instantly.
Such tools are used in the following manner: an operator places the hydraulic wrench on the nut, actuating though an impact socket. For performing the tightening or loosening, the wrench in question is fed by a high pressure hydraulic generation system (up to 700 BAR) preferably though flexible connections for increasing comfort.
When the loosening function is performed, at first and given the enormous actuating friction forces, on some occasions the nut overcomes to the friction force, instantly releasing the elastic energy stored in the bolts or screws subjected to traction (this can be 90% of the effort made). The stresses are previously balanced due to the reduced angle of the threads of the screw and the nut. When the nut is released violently it exerts a large instant impact until the friction force acts once more and balances again, the angular rotation caused by this phenomenon is very small but sufficient for damaging the pull-back system assuring that the block, the torque transmission system and the thrusting piston return together to the start position once the retraction occurs for performing another cycle. The torque transmission system of the piston is thus separated with great violence, breaking the pull-back system since it is not sized for instantaneous forces of such magnitude.
The use of fuse elements which break when the force applied by the tool exceeds a pre-established limit is known for eliminating these problems. The break of the fuse requires subsequent disassembling and replacing the parts or elements broken when the force for which they are designed is exceeded.